1. Field of the Invention
This invention relates to means for separating drops of liquid or mist entrained in a flow of gas by an improved rebound-type contacting means and particularly the invention relates to such separators having a plurality of rebound walls so arranged as to define a plurality of zig-zag or chevron shaped gas flow passages with the longitudinal axes of the walls tilted at an angle of about 45.degree. to the direction of gas flow.
2. Description of the Prior Art
Scrubbing of boiler flue gases with slurries of limestone (CaCO.sub.3) or calcined limestone products, lime and hydrate lime is a simple method to remove the sulfur dioxide from the combustion gases. Absorbers with sprays, packing or fludized beds generate liquid droplets containing solid matter of limestone or hydrated lime, calcium sulfite hydrates and calcium sulfate hydrates which must be removed from the gas stream.
Impingement type demisters have been effective in removing the liquid droplets from the flue gas stream before it is discharged to the stack and subsequent atmosphere. However, slurry droplets impinging on the demister surfaces have a natural tendency to dewater at the demister blades leaving a mud-like deposit as a residue. As more and more droplets deposit solids within the demister, it eventually becomes plugged with sludge and recrystallized sludge.
One form of mist eliminators employed in such scrubbers have separating or rebound walls which are positioned in respect to each other such that they define a plurality of zig-zag openings through which gas to be demisted passes. When a liquid-containing gas travels through such a tortuous path, the liquid droplets impinge on the surface of the separating walls and tend to stay thereon while the gas streams continue to flow through the chevron shaped passages.
The effectiveness of such mist eliminators is dependent upon many factors such as the gas velocity, the mass of the droplets, the viscosity of the gas and the geometric shape of the separating gas flow channels. Typical mist eliminators are specially suited for a particular separating task based on a known gas velocity and viscosity together with a knowledge of the size of the smallest drop which must be removed by the eliminator. It has been found that, where the gas stream contains suspended solid particles or the liquid droplets have substances dissolved therein, deposits occur on the eliminator blades which deposits alter the shape of the air flow channels, reduce the efficiency of the demisters and the operating reliability thereof. Once the deposits have started to form, the buildup of the deposition is accelerated and finally many of the separating passages become completely clogged.
It is therefore a primary object of this invention to provide an improved impingement-type mist separator having characteristics which eliminate or materially reduce the formation and buildup of deposits in the air flow channels thereof.